Small‐scale insights into superplasticity using micromechanical testing methods

In this work, the superplastic deformation behavior was investigated at the microscale as a function of temperature, strain-rate and grain-size. In detail, the superplastic alloy Zn22Al was characterized by nanoindentation at elevated temperatures, pillar compression experiments and in-situ micro tensile testing. Nanoindentation strain-rate jump tests show that the resulting strain-rate sensitivity is significantly affected by the applied strain-rate and testing temperature. The combination of these findings with the corresponding apparent activation energies evidences three different rate-controlling deformation processes, which are correlated with microstructural investigations of the residual imprints. However, significant differences regarding the deformation kinetics are observed when the size of the plastic zone is successively reduced and finally gets in the order of a few grains, giving rise to a minimum size of the plastic zone for superplastic material behavior. Via a combination of pillar compression experiments and EBSD analysis it is further suggested that superplasticity is the manifestation of a complex interaction between inter- and intra crystalline deformation processes. This behavior is discussed in detail, by taking the influence of the local phase characteristics and pillar dimension into account. Please click Additional Files below to see the full abstract

Conical Nanoindentation Allows Azimuthally Independent Hardness Determination in Geological and Biogenic Minerals

The remarkable mechanical performance of biominerals often relies on distinct crystallographic textures, which complicate the determination of the nanohardness from indentations with the standard non-rotational-symmetrical Berkovich punch. Due to the anisotropy of the biomineral to be probed, an azimuthal dependence of the hardness arises. This typically increases the standard deviation of the reported hardness values of biominerals and impedes comparison of hardness values across the literature and, as a result, across species. In this paper, we demonstrate that an azimuthally independent nanohardness determination can be achieved by using a conical indenter. It is also found that conical and Berkovich indentations yield slightly different hardness values because they result in different pile-up behaviors and because of technical limitations on the fabrication of perfectly equivalent geometries. For biogenic crystals, this deviation of hardness values between indenters is much lower than the azimuthal variation in non-rotational-symmetrical Berkovich indentations

Mechanics of colloidal supraparticles under compression

This project was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project-ID 416229255—SFB 1411

Progressive changes in crystallographic textures of biominerals generate functionally graded ceramics.

12 pagesInternational audienceBiominerals with gradually-changing crystallographic textures are an unrecognized class of elastically-graded materials that are intrinsically toughened by stress delocalisation

Negative Urgency and Emotion Regulation Strategy Use: Associations with Displaced Aggression

The numerous public health consequences of interpersonal aggression highlight the necessity of a comprehensive understanding of factors influencing its perpetration. This study examined direct and interactive associations between negative urgency and emotion regulation strategy use in predicting displaced aggression under conditions of negative mood. Participants were 197 male and female undergraduate students who were randomly assigned to employ either cognitive reappraisal or expressive suppression in response to a negative mood induction. Immediately afterward, participants engaged in an analog displaced aggression task. Results revealed direct, positive associations between negative urgency and aggression. In addition, the use of suppression was associated with greater aggression than was the use of reappraisal alone. Counter to the hypothesis, there were no interactive effects between negative urgency and emotion regulation strategy use in predicting aggression. Findings suggest reducing negative urgency and use of suppression as potential interven-tion targets for individuals who engage in aggressive behavior

High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2Re_{2}(N_{2})(N)_{2} stable at ambient conditions

High-pressure synthesis in diamond anvil cells can yield unique compounds with advancedproperties, but often they are either unrecoverable at ambient conditions or produced inquantity insufficient for properties characterization. Here we report the synthesis of metallic,ultraincompressible (K$_0$ = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8)GPa) rhenium nitride pernitride Re$_2$(N$_2$)(N)$_2$. Unlike known transition metals pernitridesRe$_2$(N$_2$)(N)$_2$ contains both pernitride N$_2$$^{4−}$ and discrete N$^{3−}$ anions, which explains itsexceptional properties. Re$_2$(N$_2$)(N)$_2$ can be obtained via a reaction between rhenium andnitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambientconditions. We develop a route to scale up its synthesis through a reaction between rheniumand ammonium azide, NH$_4$N$_3$, in a large-volume press at 33 GPa. Although metallic bondingis typically seen incompatible with intrinsic hardness, Re$_2$(N$_2$)(N)$_2$ turned to be at a thresholdfor superhard materials